The major problem in asphalt roadway repair is the current inability of the workers to obtain sufficient density and thus a proper seal upon joining new with old paving. Generally, road repairs are done on a piecemeal basis which comprises merely filling existing holes with a hot mix (asphalt composition), and compacting immediately thereafter, either manually or with a roller or tamping mechanism. Such an operation is generally performed without concern or regard to several factors which are not merely important, but rather critical in effecting a sound patch or repair. Firstly, the morphology or shape of the surface to be joined--generally the slopes of the edges on a pit or hole, are not carefully considered; and secondly, the density of the material left in the hole after compaction is rarely addressed. Where repair to be performed is a repair of a significant length of roadway, say the wheel rut areas which are cross-sectionally characterized as being most dense generally in the center of a rut and least dense at the outer crests (caused often by significant cracking and spalling), the currently used repaving methods are totally unsatisfactory.
Current teachings, typified by the patent issued to Bruns in 1982 (U.S. Pat. No. 4,364,690), attempt to solve the aforementioned problem, namely repaving an old road pavement which has been damaged by tracks or depressions worn therein. Unfortunately, there is no philosophical development as to techniques that could be used to effect a proper and controlled asphalt density after compaction; but rather, all of the patentee's attention is dedicated to the top dressing which is screeded to essentially emulate a mirror image of the damaged roadway surface. In other words, where Bruns observes a depression, he compensates by building a mound of asphalt; and where he observes generally intact paving, he lays down a mat of essentially uniform thickness and density. The most severe handicap to this method occurs when the freshly and still plastic mat is subject to a tamping form of compaction or a simple rolling compaction, because the tendency is for the higher piles of asphalt (the mounds) to be extruded and translated horizontally (and literally) past the sides of the roller or tamping mechanism. Finally, a second notable shortcoming of the Bruns methodology is the paucity of teaching regarding the case which he addresses, but never fully makes--that of fully developing a compaction philosophy that will result in a controlled density paving, thereby avoiding a repetition of the rutting that his process was initially meant to cure.
In 1980, Bruns' predecessor in the art, Lanker, was issued U.S. Pat. No. 4,181,449 for his teaching of a method and apparatus employed with a conventional paver for making a tapered joint between adjacent paved sections. Lanker generally employs a paver apparatus that comprises the modern vibratory screed. Lack of an in-depth development of compaction theory is noted in this patent; but, it is interesting for its attempt to depart from the conventional, and somewhat vertical longitudinal joint between pavement sections. From his disclosure, Lanker takes note of the density differences before various cross-sectional profiles of plastic asphalt are compacted; but, he fails to go further and relate properly the relative densities of compacted material that are realized immediately after the compaction of different cross-sectional thicknesses and shapes. On the other hand, I have noted such differences after many Years of thoroughly analyzing newly repaired or newly paved roadways which appeared to fall into acute disrepair. Quite unexpectedly, I discovered that the density acquired on a newly paved or repaired roadway section was determined not only by the amount of material mounded over the area to be paved or repaired, but responded in a most significant manner to the morphology of the top dressed and newly laid down material. Thus, I have improved upon the observations and techniques of Lanker, while avoiding the limitations in the teachings of both him and Bruns. I am able to compensate and provide a controlled density "patch" for rather extensive lengths of roadway, irrespective of whether the joint achieved is on a vertical or inclined joint. Most importantly, I have developed a methodology which flies in the teeth of conventional repaving and road maintenance techniques. In order to introduce my ideas in a technique I term Controlled Density Paving (CDP), it was necessary for me to develop specialized apparatus which, in spite of the fact that it is substantially different and used for applying my new paving techniques, appears in many respects conventional. I rely on the vibratory screed for initial tamping and, if the top dressing of the newly laid down mat is made with close attention given to the details which I inculcate herein, perhaps the only tamping or compacting that will be required in the general repaving scheme. In cases where the vibratory screed is not sufficient for imparting the desired degree of compaction to all or selected portions of the plastic asphalt mat, secondary rolling may be performed in which the desired densities will be obtained, having been acquired because of the predesignated morphology that is set out in the top dressing of the newly laid mat. The other salient piece of conventional equipment is the strike off bar or plate which is used to give the initial profiling or top dressing to the newly laid mat, traditionally a "leveling". At this point, it should be pointed out to the reader that the generally accepted term "screed" is a bit different in the asphalt laying industry than it is in the concrete paving industry. In the latter, a screed is a straight plank or bar that is run over a freshly poured surface for the purpose of leveling the freshly poured concrete slurry and, somewhat like an initial "floating", draws the water to the surface for final finishing. In asphalt paving, the strike off bar serves a purpose somewhat like the concrete screed in that it serves to level or, in some fashion, shape (top dress) a mat. The asphalt paver screed, on the other hand, acts more like a tamper or initial compaction mechanism than it does a true screed, although it too can "float" the asphalt and fine aggregate. With these distinctions in mind, I would like now to direct the reader's attention to the most current piece of relevant art that I was able to discover after an exhaustive search of patent records in the United States Patent and Trademark Office.
Watkins was issued U.S. Pat. No. 4,842,441 in June 1989 for an APPARATUS. FOR FILLING A TRENCH IN A PAVED SURFACE. This is essentially an improvement to machines for filling trenches in paved surfaces. A trench, such as that which might be effected between a paved (asphalt) road and a concrete curb is filled by the apparatus of Watkins using a vertically adjustable strike off plate (on a strike off bar) which is adapted to define a course level above or below that of the surrounding paved surface and which is used to lay down a window of paving material with a predesignated cross-sectional morphology calculated, when rolled, to fill two side mini trenches that have been created by intrusion of the paver's guide rails. A great deal of the Watkins teaching is dedicated to the type of equipment nuances that are necessary to effect the highly stylized cross-sectional profile of the asphalt window that is laid down to fill the existing trench between paving and curbside. His idea of employing plates of different sizes, attached to the strike off bar, to effect mini trenches along the sides or joints of the major trench, is highly innovative; but the plates do not lend any definition to the mat profile such that, when rolled or compacted, a controlled density of the finished mat will have been achieved. Further, the plates of Watkins move only vertically and can only adjust absolute height of a small mat portion. It is clearly evident from a reading of the Watkins disclosure that, although his apparatus clearly suits the purpose for which it was intended, it cannot rise to the level of performance needed to perform my advanced and novel Controlled Density Paving methodology. It is for this reason, that I have had to depart significantly from conventional teachings, with the hereinafter disclosed screed, strike off bars and compaction shoe apparata.